1. Field of the Invention
The present invention relates, in general, to the generation of channel information and the transmission of data using the channel information, and, more particularly, to a channel information generation apparatus and method for Spatial Division Multiplexing (SDM) in a wireless communication system and a data transmission apparatus and method using generated channel information, which generate channel information using frequency correlations between the channels of adjacent subcarriers, transmit the generated channel information to the transmitter, and allow the transmitter to generate a precoding matrix on the basis of the received information and to transmit data using SDM so that data can be transmitted using SDM in an Orthogonal Frequency Division Multiplexing (OFDM)-based wireless communication system that uses Multiple-Input Multiple-Output (MIMO) antennas.
2. Description of the Related Art
In a wireless communication system that uses Multiple-Input Multiple-Output (MIMO) antennas, when a transmitter can use channel information, system capacity can be greatly increased using an SDM transmission method combined with a precoding technique (A. Scaglione, P. Stoica, S. Barbarossa, G. B. Giannakis, and H. Sampath, “Optimal designs for space-time linear precoders and decoders,” IEEE Trans. Signal Process., vol. 50, no. 5, pp. 1051-1064, May 2002.).
In this case, when an uplink channel and a downlink channel are not reciprocal as in the case of Frequency Division Duplexing (FDD), a transmitter can obtain channel information from the receiver. Here, the channel information can be obtained using a quantization technique such as a Grassmannian codebook technique so as to reduce the amount of feedback signal information (D. J. Love, and R. W. Heath Jr., “Limited feedback unitary precoding for spatial multiplexing systems,” IEEE Trans. Inform. Theory, vol. 51, no. 8, pp. 2967-2976, August 2005.).
Such a codebook-based technique adopts a scheme for searching a codebook, which contains channel information predefined by a transmitter/receiver, for optimal channel information, and feeding index information corresponding to the optimal channel information back to the transmitter. In particular, a Grassmannian codebook technique can efficiently generate a codebook using a small amount of information in consideration of the characteristics of a precoding matrix being independent of phase.
Meanwhile, an OFDM technique is advantageous in that MIMO techniques can be easily applied thereto because a frequency-selective channel environment can be converted into a plurality of frequency non-selective environments. Accordingly, recently, research into MIMO-OFDM systems in which a MIMO technique is combined with an OFDM technique to obtain a high transfer rate has been widely conducted.
In such a MIMO-OFDM system, in order to implement an SDM technique combined with a precoding technique, a transmitter needs to obtain channel information about each subcarrier from the receiver. Accordingly, the amount of feedback burden required to obtain channel information increases in proportion to the number of subcarriers that are used. An example of a method of reducing such a feedback burden may include a method of gathering a plurality of adjacent subcarriers into one cluster and feeding back only channel information corresponding to the representative subcarrier of the cluster. This clustering technique can reduce the amount of feedback information in proportion to the size of the cluster, but is disadvantageous in that as the size of the cluster increases, system performance is reduced.
As a method of overcoming the disadvantage of reduced system performance, research into an interpolation-based technique using interpolation has been conducted (J. Choi and R. W. Heath, Jr., “Interpolation based unitary precoding for spatial multiplexing MIMO-OFDM with limited feedback,” IEEE Trans. Signal. Process., vol. 54, no. 12, pp. 4730-4740, August 2006). However, such an interpolation technique is disadvantageous in that when a Grassmannian codebook is used, phase information for interpolation is additionally required due to the characteristics of the codebook being independent of phase, thus increasing the amount of feedback information.
Recently, in order to compensate for the disadvantages of an interpolation technique, a technique for reducing the amount of feedback information using correlations between adjacent subcarriers among OFDM subcarriers has been proposed (S. Zhou, B. Li and P. Willett, “Recursive and trellis-based feedback reduction for MIMO-OFDM with rate-limited feedback,” IEEE Trans. Wireless Commun., vol. 5, no. 12, pp. 3400-3405, December 2006). However, a problem still remains in that as the number of subcarriers increases, the amount of feedback information increases.